1. Field of the Invention
The invention relates to endoscopic instruments. More particularly, the invention relates to electrocautery probes for use with a resectoscope or hysteroscope and specifically relates to roller electrodes used in electrocautery probes.
2. State of the Art
Electrosurgical resection is a procedure in which damaged or enlarged tissue is excised with an electrocautery probe. Transurethral resection is an electrosurgical procedure in which a portion of the prostrate is excised by means of an instrument passed through the urethra. Endometrial ablation is an electrosurgical alternative procedure to hysterectomy for women with menorrhagia (abnormal or excessive uterine bleeding). In these procedures, the instrument typically used is called a resectoscope or hysteroscope. Prior art FIG. 1 shows a typical resectoscope 10 with an electrocautery probe 12. The resectoscope 10 includes a distal guide tube 14 and a proximal handle 16. A telescope 18 is inserted through the guide tube 14 and is provided with a proximal eye piece 20 for viewing the interior of the bladder or other operative site. The cautery probe 12 has a distal electrode 22 which is mounted between a pair of arms 23, 25. The arms 23, 25 are joined at their proximal ends to an electrode lead 27 which is coupled via the handle 16 to a wire 24 which is coupled to a source of cautery current (not shown). A mounting sleeve 29 is provided on the probe 12 for slideably coupling it to the guide tube 14. The mounting sleeve 29 is typically located at the point where the arms 23, 25 are joined to the electrode lead 27. The handle 16 is generally capable of axially sliding the probe 12 and its distally mounted electrode 22 relative to the guide tube 14.
The ablation or resection procedure involves applying a cauterizing voltage to the electrode 22 and moving the electrode slowly over the prostate or endometrium while viewing the tissue through the scope 18. Thermal energy is applied through the electrode to the prostate or the endometrium so that tissue is excised. The resectoscope and cautery probe are also useful in other procedures for resecting the uterus, ureter, or renal pelvis.
Known electrodes for use in resectoscopes are available in many different shapes and sizes. U.S. Pat. No. 4,917,082 to Grossi et al., for example, discloses several embodiments of a "Resectoscope Electrode" including a coagulating electrode, a knife electrode, a punctate electrode, and a roller electrode, among others. Electrodes for use with resectoscopes are also widely available from Olsen Electrosurgical, Inc., Concord, Calif. They are available as blades, needles, balls, loops, spear tips, flexible wires, semi-circular wires, hooks, spatulas and blunt tips.
Recently, the generally preferred electrode for use in endometrial ablation is the roller (often referred to as "roller bar" or "roller ball") electrode. Prior art FIGS. 1 and 2 show a roller bar electrode 22. The roller bar is approximately 2.5 mm long and has a central bore 22b. It is rotatably mounted between the arms 23, 25 at the distal end of the electrocautery probe 12 by means of an axle wire 21 which extends through the central bore 22b of the electrode 22. The roller bar is supplied with a cauterizing voltage through the wire 21 which is coupled to the arms 23, 25 in the probe 12. When energized, the electrode 22 is rolled across the endometrial surface methodically until desired areas of the endometrium have been ablated. Roller bar electrodes are also used in prostatic resection. It is generally appreciated that in both endometrial ablation and prostatic resection, a larger surface area will allow the electrode to cover more tissue and thereby shorten the procedure. It is also understood that in the case of prostatic resection, the overall size of the electrode (as well as the resectoscope) must be kept to a minimum. Thus, it is difficult to increase the surface area of the electrode while maintaining a small overall size. One known way of providing increased electrode surface area while maintaining a small overall size is disclosed in co-owned U.S. Pat. No. 5,354,296 which describes a variable morphology electrode. Another way of providing increased electrode surface area while maintaining a small overall size is to provide radial or helical grooves in the surface of the roller bar. Prior art FIG. 3 shows an electrocautery probe 112 which is fitted with a roller electrode 122 having a helical groove 122a. The groove effectively increases the surface area of the electrode without increasing its overall size. However, the resulting roller electrode lacks traction and tends to glide over the tissue rather than rolling. This causes tissue to accumulate on the surface of the electrode and interfere with the surgical procedure.